On unsealed roads and in particularly mine haul roads, it is necessary to spray water on the roads in order to reduce the amount of dust generated by vehicles travelling over these roads. Where the amount of water sprayed onto a road is not managed correctly, there is a tendency for the road to be either over watered or under watered. Over watering can make the unsealed roads slippery and more difficult to negotiate resulting in vehicle accidents, longer journey times and therefore increased time moving the product from source to destination. This results in an overall reduction in the productivity of the road itself.
In contrast, under watering can result in health issues to the drivers and other employees due to the poor control of dust spread by the use of the vehicles on the road. Furthermore, at many mine sites, water is a valuable and rare asset and poor water spraying practices consequently wastes the valuable water resource with no real benefit.
In order to manage the water, a useful spraying practice is to spread water on the unsealed roads at a rate relative to the ground speed ie. a constant rate or a pre-calibrated rate irrespective of the vehicle speed. In simple terms, as the vehicle speeds up, more water is sprayed from the vehicle. As the vehicle slows down, less water is sprayed. This results in a constant water rate being sprayed onto the ground providing a constant water coverage on the ground.
One method to control the water spray rate and provide a constant coverage on the ground is to control the speed of the hydraulic motor driving the water pump using electronics relative to the ground speed. This controls the water pressure exiting the water pump. As the water is delivered onto the road by a fixed orifice, the amount of water delivered through the orifice varies according to the pressure which is in turn dictated by the speed of the vehicle. This method requires a considerable and expensive amount of changes to the hydraulic drive system that runs the water pump.
The problem of providing a set rate of liquid spray coverage from a vehicle is also present in the agricultural industry where chemicals mixed in a tank on a vehicle need to be sprayed at predetermined spray coverage rates. While the invention has been directed to the spraying of water from a vehicle, the invention is also applicable to other applications of liquid from a moving vehicle such as the spraying of agricultural chemicals.
It is an object of the invention to provide a liquid delivery system which is an alternative to those previously provided:
Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.